Venturi vents feature a contemporary horizontal louvered design that adds a clean look to any boat. These patented vents are sized for easy installation, even on highly-contoured decks. ABS plastic construction will not corrode or discolor. For 3 or 4 ID ventilation system. Requires ATT 1341-1 collector box for 3 system, or ATT 1342-1 special order only for 4 system Above-deck dimensions: 2- 3/4 W x 17- 9/16 L x 11/16 H Pre-drilled with four holes for 8 screws